Supercritical water oxidation (SCWO) has been demonstrated to be effective in the destruction of hazardous and toxic wastes. This chemical oxidation process takes place at temperatures above 374.15.degree. C. and 22.1 MPa. Supercritical water acts as a dense gas, with the solvation characteristics of a nonpolar organic solvent; organic material and gases are miscible with supercritical water, yet inorganic salts are virtually insoluble. High destruction efficiencies (&gt;99.99%) over relatively short residence times (on the order of seconds to minutes) are achieved due to the high solubility of organic compounds and oxygen, alleviating mass transfer hindrances. Typically, at supercritical conditions, complete conversion results in carbon dioxide, water, and mineral acids. However, under moderate SWCO conditions, (such as, lower temperatures, shorter residence times and limited amounts of oxidant), some refractory intermediates (e.g., acetic acid, ammonia, or carbon monoxide) have been observed in the reactor effluent. These and other possible reaction intermediates may be useful in themselves or as raw materials in chemical synthesis.
For example, carbon monoxide (CO) and hydrogen (H.sub.2) are of commercial interest to the production of synthesis gas (syn gas), a starting material for various chemical syntheses. Three methods are used industrially for generating syn gas: steam reforming of methane; partial oxidation of heavy fuel oil; and coal gasification; for these methods, once a procedure is chosen, the ratio of CO to H.sub.2 obtained in the off-gas is typically fixed at a CO/H.sub.2 molar ratio of 1/3, 1/1, and 2/1, respectively. Conventionally, the ratio of CO/H.sub.2 may be altered via the water gas shift reaction (also called CO conversion reaction): EQU CO+H.sub.2 O.revreaction.H.sub.2 +CO.sub.2
This reaction may be used to shift the H.sub.2 /CO ratio in synthesis gas or to alter H.sub.2 production.
U.S. Pat. No. 4,251,227 relates to a method for producing substitute natural gas or syn gas from wet solid wastes and low grade fuels under subcritical conditions. U.S. Pat. No. 5,250,193 relates to wet oxidation for destruction of organic components in a wastewater stream contaminated with inorganic salts. U.S. Pat. No. 3,716,474 relates to high pressure thermal treatment of waste oil-containing sludges. U.S. Pat. No. 4,465,888 relates to oligomerization of olefins in supercritical water. U.S. Pat. Nos. 4,594,141 and 4,840,725 relate to the conversion of high boiling organic materials to low boiling materials. U.S. Pat. No. 5,133,877 relates to conversion of hazardous materials using supercritical water oxidation. U.S. Pat. No. 4,483,761 relates to upgrading heavy hydrocarbons with supercritical water and light olefins, and U.S. Pat. No. 5,232,604 relates to a process for the oxidation of materials in water at supercritical temperatures utilizing reaction rate enhancers.
Japanese Patent JP 5031000 relates to a method comprising selectively hydrolysing and/or pyrolysing natural or synthetic high molecular compounds using water under supercritical or subcritical conditions as solvent. Brazilian Patent BR 8204075 and Australian Patent application 8285597 relate to the production of synthesis gas carried out by pretreatment of feedstock under subcritical wet oxidation conditions to convert organic materials to carbon dioxide that is then fed to an existing syn gas producer, either a steam reformer or a partial oxidation gasifier. The reported improvement relates to reducing and controlling the H.sub.2 /CO ratio in the synthesis gas by wet oxidizing combustible materials to obtain a gas comprising a mixture of water vapor and carbon dioxide.
Holgate et al. relates to the determination of new kinetic parameters for the water-gas shift reaction and for the direct oxidation of carbon monoxide in supercritical water.
The prior art methods of producing syn gas each have the disadvantage of lacking any control in achieving a particular ratio of CO/H.sub.2. A further disadvantage of prior art methods is the loss of carbon as CO.sub.2 due to the water gas shift reaction.